fix(cli): reject execute() immediately when child process is dead

When a child process crashes and a retry is attempted on the same
TaskRunProcess, execute() would hang forever because the IPC send
was silently skipped and the attempt promise could never resolve.
This caused runner pods to stay up indefinitely with no heartbeats.

Author: nicktrn

.changeset/fix-dead-process-execute-hang.md

@@ -0,0 +1,5 @@
+---
+"trigger.dev": patch
+---
+
+Fix runner getting stuck indefinitely when `execute()` is called on a dead child process.

packages/cli-v3/src/executions/taskRunProcess.test.ts

@@ -0,0 +1,121 @@
+import { TaskRunProcess, type TaskRunProcessOptions } from "./taskRunProcess.js";
+import { describe, it, expect, vi } from "vitest";
+import { UnexpectedExitError } from "@trigger.dev/core/v3/errors";
+import type {
+  TaskRunExecution,
+  TaskRunExecutionPayload,
+  WorkerManifest,
+  ServerBackgroundWorker,
+  MachinePresetResources,
+} from "@trigger.dev/core/v3";
+
+function createTaskRunProcessOptions(
+  overrides: Partial<TaskRunProcessOptions> = {}
+): TaskRunProcessOptions {
+  return {
+    workerManifest: {
+      runtime: "node",
+      workerEntryPoint: "/dev/null",
+      configEntryPoint: "/dev/null",
+      otelImportHook: {},
+    } as unknown as WorkerManifest,
+    serverWorker: {} as unknown as ServerBackgroundWorker,
+    env: {},
+    machineResources: { cpu: 1, memory: 1 } as MachinePresetResources,
+    ...overrides,
+  };
+}
+
+function createExecution(runId: string, attemptNumber: number): TaskRunExecution {
+  return {
+    run: {
+      id: runId,
+      payload: "{}",
+      payloadType: "application/json",
+      tags: [],
+      isTest: false,
+      createdAt: new Date(),
+      startedAt: new Date(),
+      maxAttempts: 3,
+      version: "1",
+      durationMs: 0,
+      costInCents: 0,
+      baseCostInCents: 0,
+    },
+    attempt: {
+      number: attemptNumber,
+      startedAt: new Date(),
+      id: "deprecated",
+      backgroundWorkerId: "deprecated",
+      backgroundWorkerTaskId: "deprecated",
+      status: "deprecated" as any,
+    },
+    task: { id: "test-task", filePath: "test.ts" },
+    queue: { id: "queue-1", name: "test-queue" },
+    environment: { id: "env-1", slug: "test", type: "DEVELOPMENT" },
+    organization: { id: "org-1", slug: "test-org", name: "Test Org" },
+    project: { id: "proj-1", ref: "proj_test", slug: "test", name: "Test" },
+    machine: { name: "small-1x", cpu: 0.5, memory: 0.5, centsPerMs: 0 },
+  } as unknown as TaskRunExecution;
+}
+
+describe("TaskRunProcess", () => {
+  describe("execute() on a dead child process", () => {
+    it("should reject when child process has already exited and IPC send is skipped", async () => {
+      const proc = new TaskRunProcess(createTaskRunProcessOptions());
+
+      // Simulate a child process that has exited: _child exists but is not connected
+      const fakeChild = {
+        connected: false,
+        killed: false,
+        pid: 12345,
+        kill: vi.fn(),
+        on: vi.fn(),
+        stdout: { on: vi.fn() },
+        stderr: { on: vi.fn() },
+      };
+
+      // Set internal state to mimic a process whose child has crashed
+      (proc as any)._child = fakeChild;
+      (proc as any)._childPid = 12345;
+      (proc as any)._isBeingKilled = false;
+
+      const execution = createExecution("run-1", 2);
+
+      // This should NOT hang forever - it should reject promptly.
+      //
+      // BUG: Currently execute() creates a promise, skips the IPC send because
+      // _child.connected is false, then awaits the promise which will never
+      // resolve because the child is dead and #handleExit already ran.
+      //
+      // The Promise.race with a timeout detects the hang.
+      const result = await Promise.race([
+        proc
+          .execute(
+            {
+              payload: { execution, traceContext: {}, metrics: [] },
+              messageId: "run_run-1",
+              env: {},
+            },
+            true
+          )
+          .then(
+            (v) => ({ type: "resolved" as const, value: v }),
+            (e) => ({ type: "rejected" as const, error: e })
+          ),
+        new Promise<{ type: "hung" }>((resolve) =>
+          setTimeout(() => resolve({ type: "hung" as const }), 2000)
+        ),
+      ]);
+
+      // The test fails (proving the bug) if execute() hangs
+      expect(result.type).not.toBe("hung");
+      expect(result.type).toBe("rejected");
+
+      if (result.type === "rejected") {
+        expect(result.error).toBeInstanceOf(UnexpectedExitError);
+        expect(result.error.stderr).toContain("not connected");
+      }
+    });
+  });
+});

packages/cli-v3/src/executions/taskRunProcess.ts

@@ -297,6 +297,19 @@ export class TaskRunProcess {
         env: params.env,
         isWarmStart: isWarmStart ?? this.options.isWarmStart,
       });
+    } else {
+      // Child process is dead or disconnected — the IPC send was skipped so the attempt
+      // promise would hang forever. Reject it immediately to let the caller handle it.
+      this._attemptStatuses.set(key, "REJECTED");
+
+      // @ts-expect-error - rejecter is assigned in the promise constructor above
+      rejecter(
+        new UnexpectedExitError(
+          -1,
+          null,
+          "Child process is not connected, cannot execute task run"
+        )
+      );
     }
 
     const result = await promise;